Surveying underground structures



July 28, 1936. a. B. wEA'rHERBY 4 SURVEYING UNDERGROUND STRUCTURES Filed OCT.. 27, 1934 /N VENTO-R `A T ORNE Y;

.vallfllll Patented July 28, 1936 PATENT 2,049,236 SURVEYING UNDERGROUND STRUCTURES Benjamin B. Weatherby, Tulsa, Okla., assignor to Geophysical Research Corporation, New York, N. Y., a corporation of New Jersey Application October 2.7, 1934, Serial No. 750,276 9 Claims. (Cl. ISI-0.5)

f In the method of surveying underground struc tures commonly known as the seismic method, artificial seismic waves are created by detonating a charge of explosive at ornear the earth's surface and the travel times of the reflected and refracted waves to points distant from the wave source are measured by means of suitable wavereceiving and recording apparatus. The explosive charge usually is placed at the bottom of a drilled hole which may be located from 10 to 15th/feet in depth. It has been found that the character oi wave records thus obtained is often dependent upon the type of material in which the explosive is detonated and that the eifectivenessof a given charge of explosive is also dependent upon the vmaterial in which it is planted. Because of this dependence, it is difficult to obtain satisfactory records in certain areas. For example, in many areas in which it is desired to make a seismic survey, the material at ornear the surface of the earth is sandy in nature. When shot holes are dug in such material, itis necessary to use relatively large charges oi' explosive to obtain usable records. Furthermore, the records are quite often unsatisfactory because the presence of sand about the shot hole vhas a deleterious eifect upon the character of the wave produced by the explosion of the charge.

An object of this invention is -to largely eliminate the eects above referred to.

In the practice of the method of this invention, a shot hole is bored in the usual fashion. A material different from that naturally surrounding the hole is -introduced the bottom of thev hole and a new hole is drilled in such material. The explosive charge is thus introduced into the new hole and detonated to produce seismic waves for recording in the customary manner. Preferably. the bottomof the shot hole is enlarged before introduction thereinto of material different from that naturally surrounding fthe hole. Such enlargement of the bottom of the hole may be eected by lowering a charge of explosive to the bottom of the hole and detonating itin order to produce a cavity. y

'I'he type of material chosen vfor introduction into the cavity is determined both by the character of the natural material in which the hole is dug and by the type of results which are desired. In the specific case previously mentioned, if a shot hole is dug in sand any one of several materials may be introduced into the cavity. A satisfactory material consists of a mixture of rapid hardening Portland cement and bentonite.

' Another'suitable material is a mixture of clay terial" are used in the claims to denne any maand water such as is commonly used in drilling oil wells by the rotary drill method. Such material is preferably introduced in sumcient quantity to entirely fill the cavity atthe bottom of the hole and to extend some distance up the hole. After the introduced material has hardened or sufliciently solidified by settling, a new hole is drilled therein.

Referring now to the drawing wherein the singie figure diagrammatically illustrates a bore hole made according to the invention, the upper portion of the original bore hole is designated by the reference character illa. The lower portion lub of the bore hole is drilled into material li introduced into a cavity formed at the bottom of the drill hole. This material is different than the material in which the cavity is made and preferably is of greater density and greater compactness than the material in which the cavity is formed. The explosive charge i2 is then lowered 20 to the bottom of the bore hole and is detonated in theusual manner by means of thering mechanism I3.

It often happens that the shot hole is dug into a limestone which is badly shattered and creviced. In such event, the materials previously mentioned may be introduced into the bottom of the hole to form a compact mass into which the bore hole is extended as above described.

In some cases, where the shot hole is formed in earth of greater density than sand, it may he desirable to alter the character of the wave front produced by the detonation of an explosive charge so as to reduce the percentage of energy contained in the higher frequency components. Such alteration in the wave front may be produced by using sand or similar granular material to fill the cavity at the bottom of the shot hole. In any use of the method, material of different composition than the material in which the bore hole is made is introduced into the bottom of the bore hole and a .new hole is made in such material in which the explosive'charge is arranged and detonated. Preferably, the bottom of the bore hole is first enlarged to form a cavity within which is 'received the material of different composition than the material of which the cavity is made, but in some instances, particularly when a small charge of Vexplosive is to be used, it may not be necessary-to form a cavity at the bottom of the hole and in such a case, the material is introduced into the bottom of the original hole and a new hole of smaller diameter is drilled in the introduced material. The words solid material of suiilcient stability to permit a hole being formed therein and are intended to cover plastic material as well asrigid material.

I claim: 1. The method of creating artificial seismic waves for use in sub-surface surveying which comprises conditioning a shot hole formed in sandy soil by i'orming a cavity at the bottom of the hole, introducing into the cavity a mixture .of quick-hardening cement and bentonite, extending the shot hole into the introduced material and detonating an explosive charge in the extension of said hole.

2. The method of creating artificial seismic waves for use in sub-surface surveying which comprises drilling a hole, filling the lower portion of said hole with solid material different from that in which the hole is drilled, drilling a hole comprises conditioning shot holes'formed in the earth by illling the lower portion of the hole with solid material different than the earth in which -the hole is formed, drillinga new hole in such material. and detonating an explosive charge in said new hole.

5. The method of creating articial seismic waves for use in sub-surfacev surveying which comprises drilling a hole. enlarging the bottom 4 of the hole, iilling the enlargement with solid material diierent from the material in which the enlargement is made, extending the hole into the filled-in material and detonatingan explosive charge in the extension of said hole.

6. The method of creating artificial seismic 5 waves for use in sub-surface surveying which comprises drilling a hole, enlarging the bottom of the hole, lling such enlargemcnt'with solid material of greater density than the material inwhich the enlargement is made, extending the hole into the lled-in material and detonatingl an explosive charge in the extension of said ho e.

7. The method of creating artiilcial seismic waves for use in `sub-surface surveying which 15 comprises drilling a hole, enlarging the bottom of the hole, iilling the enlargement with solid material of greater compactness than the material of which the enlargement is made, extending the hole into the lled-in material, and detonating an explosive charge in the extension of said hole.

8. 'I'he method of creating articial seismic waves for use in sub-surface surveying which comprises conditioning shot holes formed in 25 sandy earth by enlarging the bottom of the hole, lling the enlargement with solid material of Agreater density than the earth in which the hole is formed. extending the hole into the illled-in material and detonating an explosive charge in` 30 

